Issue #3413043 by pdureau: Improve compatibility with existing SDC themes

modules/ui_patterns_legacy/src/ComponentConverter.php

modules/ui_patterns_legacy/src/PropConverter.php

modules/ui_patterns_legacy/src/RenderableConverter.php

.../ui_patterns_library/src/Controller/LibraryController.php

...ibrary/templates/ui-patterns-component-metadata.html.twig

modules/ui_patterns_library/ui_patterns_library.routing.yml

src/Element/ComponentElement.php

src/Plugin/UiPatterns/PropType/EnumListPropType.php

src/Plugin/UiPatterns/PropType/LinksPropType.php

src/Plugin/UiPatterns/PropType/ListPropType.php

src/Plugin/UiPatterns/PropType/UnknownPropType.php

src/Plugin/UiPatterns/Source/ChecboxesWidget.php

src/Plugin/UiPatterns/Source/ListTextareaWidget.php

src/PropTypePluginManager.php

src/SchemaManager/Canonicalizer.php

src/SchemaManager/CompatibilityChecker.php

...omponents/prop_types_tests/prop_types_tests.component.yml

...ns_test/components/prop_types_tests/prop_types_tests.twig